Methods for reducing or preventing transplant rejection in the eye and intraocular implants for use

ABSTRACT

Methods for reducing or preventing transplant rejection in the eye of an individual are described, comprising: a) performing an ocular transplant procedure; and b) implanting in the eye a bioerodible drug delivery system comprising an immunosuppressive agent and a bioerodible polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser. No. 10/744,560, now U.S. Pat. No. 7,033,605, filed Dec. 22, 2003, which is a continuation application of U.S. application Ser. No. 09/997,094, filed Nov. 28, 2001, now U.S. Pat. No. 6,699,493, which claims the benefit of U.S. Provisional Application No. 60/250,023, filed Nov. 29, 2000 and U.S. Provisional Application No. 60/298,253, filed Jun. 12, 2001. The disclosure of each of these applications is incorporated in its entirety herein by reference.

TECHNICAL FIELD

This invention relates to the field of transplantation, in particular transplantation of components of the eye, and methods for preventing transplant rejection.

BACKGROUND ART

Certain conditions and diseases of the eye, such as corneal failure, keratoconus, corneal dystrophies, scarring, age related macular degeneration (AMD) and retinitis pigmentosa, have been treated using ocular transplant procedures such as corneal and retinal pigment epithelial (RPE) transplants. Transplant rejection is one of the problems which may arise from transplant procedures (Enzmann V et al. (1998). “Immunological problems of transplantation into the subretinal space.” Acta Anat (Basel). 162(2-3): 178-83). In spite of the overall success with corneal transplants, a substantial percentage of corneal grafts experience at least one rejection episode (PCT/US97/21393).

One of the problems with present immunosuppressive drug therapy is the inability to achieve adequate intraocular drug concentrations. Systemic immunosuppression may require prolonged exposure to high plasma concentrations so that therapeutic levels can be achieved in the eye. Overall drug delivery to the eye may be poor due to the short drug plasma half-life limiting exposure into intraocular tissues. In addition, this may turn lead to numerous negative side effects.

There is a continued need for improved intraocular sustained release drug therapies for patients following ocular transplant procedures.

All references cited in this patent are incorporated herein by reference in their entirety.

DISCLOSURE OF THE INVENTION

One embodiment of the present invention provides a method for reducing or preventing transplant rejection in the eye of an individual, where the method comprises: a) performing an ocular transplant procedure; and b) implanting in the eye a bioerodible drug delivery system comprising an immunosuppressive agent and a bioerodible polymer.

Another embodiment of the invention provides a method for reducing or preventing transplant rejection in the eye of an individual, where the method comprises: a) performing an ocular transplant procedure; and b) implanting a solid body into the eye, said body comprising particles of an immunosuppressive agent entrapped within a bioerodible polymer, whereby said agent is released from the body by erosion of the polymer.

Another embodiment of the invention provides a method which includes placing in an eye of an individual a bioerodible drug delivery system, where the bioerodible drug delivery system includes an immunosuppressive agent and a bioerodible polymer; and where the eye of the individual has undergone or is undergoing an ocular transplant procedure. This method may be used to reduce or prevent transplant rejection.

Another embodiment of the invention provides a kit comprising: a) a bioerodible drug delivery system comprising an immunosuppressive agent and a bioerodible polymer, wherein the drug delivery system is designed to be implanted in the eye; and b) instructions for use. This kit may be used to reduce or prevent transplant rejection.

MODES FOR CARRYING OUT THE INVENTION

Definitions

An “ocular transplant procedure,” as used herein, refers to any transplant procedure performed in the eye. Non-limiting examples of ocular transplant procedures include, but are not limited to, retinal pigment epithelium (RPE) transplant and cornea transplant. It includes autograft, allograft and xenograft transplant procedures.

“Immunosuppressive agent,” “agent,” “immunosuppressive drug,” and “drug,” are used interchangeably herein, and refer to any agent which inhibits or prevents an immune response against the transplanted tissue following a transplant procedure. Exemplary agents include, but are not limited to, dexamethasone, cyclosporin A, azathioprine, brequinar, gusperimus, 6-mercaptopurine, mizoribine, rapamycin, tacrolimus (FK-506), folic acid analogs (e.g., denopterin, edatrexate, methotrexate, piritrexim, pteropterin, Tomudex®, trimetrexate), purine analogs (e.g., cladribine, fludarabine, 6-mercaptopurine, thiamiprine, thiaguanine), pyrimidine analogs (e.g., ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, doxifluridine, emitefur, enocitabine, floxuridine, fluorouracil, gemcitabine, tegafur), fluocinolone, triaminolone, anecortave acetate, flurometholone, medrysone, and prednislone.

An “implant” and a “drug delivery system,” are used interchangeably herein, and include any bioerodible device for implantation in the eye which is capable of delivering a therapeutic level of drug to the eye.

To “implant” to “place” and to “insert” are equivalent as used in this patent and mean to place an object in the desired site by any means capable of placing the object at that site.

By “therapeutic level” is meant a level of drug sufficient to prevent, inhibit, or reduce the level of transplant rejection in the eye.

The term “bioerodible polymer” refers to polymers which degrade in vivo, and wherein erosion of the polymer over time is required to achieve the agent release kinetics according to the invention. Specifically, hydrogels such as methylcellulose which act to release drug through polymer swelling are specifically excluded from the term “bioerodible polymer”. The terms “bioerodible” and “biodegradable” are equivalent and are used interchangeably in this patent.

An “individual” is a vertebrate, preferably mammal, more preferably a human. Mammals include, but are not limited to, humans, rodents, sport animals and pets, such as rats, dogs, and horses.

Methods for Reducing or Preventing Transplant Rejection

Intraocular immunosuppressive drug delivery systems made of a biodegradable polymer matrix are provided which can release drug loads over various programmed time periods. When inserted into the eye these drug delivery systems provide therapeutic levels of immunosuppressive agent for reducing or preventing transplant rejection.

Accordingly, one embodiment of the present invention provides a method for reducing or preventing transplant rejection in the eye of an individual, comprising: performing an ocular transplant procedure; and implanting in the eye a bioerodible drug delivery system comprising an immunosuppressive agent and a bioerodible polymer.

In another embodiment of the invention, a method for reducing or preventing transplant rejection in the eye of an individual is provided, comprising: performing an ocular transplant procedure; and implanting a solid body into the eye, said body comprising particles of an immunosuppressive agent entrapped within a bioerodible polymer, whereby said agent is released from the body by erosion of the polymer.

Ocular transplant procedures which may be used with the methods of the invention include, but are not limited to, cornea transplant and RPE transplant. Methods for performing these transplant procedures are well known in the art. Methods for performing RPE transplants are described in, for example, U.S. Pat. Nos. 5,962,027, 6,045,791, and 5,941,250 and in Eye Graefes Arch Clin Exp Opthalmol 1997 March; 235(3):149-58; Biochem Biophys Res Commun 2000 Feb. 24; 268(3): 842-6; Opthalmic Surg 1991 February; 22(2): 102-8. Methods for performing corneal transplants are described in, for example, U.S. Pat. No. 5,755,785, and in Eye 1995; 9 (Pt 6 Su):6-12; Curr Opin Opthalmol 1992 August; 3 (4): 473-81; Ophthalmic Surg Lasers 1998 April; 29 (4): 305-8; Ophthalmology 2000 April; 107 (4): 719-24; and Jpn J Ophthalmol 1999 November-December; 43(6): 502-8. Exemplary methods for corneal and RPE transplantation in animal models are described in Examples 1, 4 and 5 below. In a preferred embodiment, the ocular transplant procedure is a cornea transplant. In another preferred embodiment, the ocular transplant procedure is an RPE procedure.

The drug delivery system may be implanted at various sites in the eye, depending on the size, shape and formulation of the implant, the type of transplant procedure, etc. Suitable sites include but are not limited to the anterior chamber, anterior segment, posterior chamber, posterior segment, vitreous cavity, suprachoroidal space, subconjunctiva, episcleral, intracorneal, epicorneal and sclera. In a preferred embodiment, the drug delivery system is placed in the anterior chamber of the eye. In another preferred embodiment, the drug delivery system is placed in the vitreous cavity.

The implants may be inserted into the eye by a variety of methods, including placement by forceps or by trocar following making an incision in the sclera (for example, a 2-3 mm incision) or other suitable site. In some cases, the implant may be able to be placed by trocar without making a separate incision, but instead by punching a hole directly into the eye with the trocar. The method of placement may influence the drug release kinetics. For example, implanting the device into the vitreous with a trocar may result in placement of the device deeper within the vitreous than placement by forceps, which may result in the implant being closer to the edge of the vitreous. The location of the implanted device may influence the concentration gradients of drug surrounding the device, and thus influence the release rates (e.g., a device placed closer to the edge of the vitreous may result in a slower release rate).

U.S. Pat. No. 5,869,079 further describes locations for intraocular implants and methods for insertion (see in particular col. 6-7).

In one embodiment, the implant delivers the immunosuppressive agent for at least about 5 days. In other embodiments, the implant delivers the immunosuppressive agent for at least about one week, at least about 2 weeks, at least about 3 weeks, at least about four weeks, at least about five weeks, at least about six weeks, at least about seven weeks, at least about eight weeks, at least about nine weeks, at least about 10 weeks, and at least about 12 weeks. The preferred duration of drug release may be determined by the type of transplant, the medical history of the patient, etc. In one embodiment, drug release may occur for up to 6 months, or one year, or longer. In one embodiment, more than one implant may be sequentially implanted into the vitreous in order to maintain drug concentrations for even longer periods. In one embodiment, more than one implant may be sequentially implanted into the eye in order to maintain therapeutic drug concentrations for longer periods. Co-owned U.S. patent application Ser. No. 09/693,008, titled “Methods For Treating Inflammation-Mediated Conditions of the Eye,” to Wong et al. filed Oct. 20, 2000, which is expressly incorporated herein by reference in its entirety, further describes implants and methods for making the implants which can achieve and maintain particular drug concentrations for programmed extended periods of time.

The methods of the invention are preferably performed on vertebrates, preferably mammal, more preferably a human. Mammals include, but are not limited to, humans, rodents, sport animals and pets, such as rats, dogs and horses.

Implants

The formulation of the implants for use in the invention may vary according to the preferred drug release profile, the particular immunosuppressive agent used, the transplant procedure, the medical history of the patient and other factors affecting the formulation.

The implants of the invention are formulated with particles of the immunosuppressive agent associated with the bioerodible polymer matrix. In a preferred embodiment the immunosuppressive agent is entrapped within the bioerodible polymer matrix. Without being bound by theory, we hypothesize that release of the agent is achieved by erosion of the polymer followed by exposure of previously entrapped agent particles to the eye, and subsequent dissolution and release of agent. The release kinetics achieved by this form of drug release are different than that achieved through formulations which release drug through polymer swelling, such as with hydrogels such as methylcellulose. In that case, the drug is not released through polymer erosion, but through polymer swelling, which release drug as liquid diffuses through the pathways exposed. The parameters which may determine the release kinetics include the size of the drug particles, the water solubility of the drug, the ratio of drug to polymer, the method of manufacture, the surface area exposed, and the erosion rate of the polymer.

In a preferred embodiment the immunosuppressive agent is selected from the group consisting of dexamethasone, cyclosporin A, azathioprine, brequinar, gusperimus, 6-mercaptopurine, mizoribine, rapamycin, tacrolimus (FK-506), folic acid analogs (e.g., denopterin, edatrexate, methotrexate, piritrexim, pteropterin, Tomudex®, trimetrexate), purine analogs (e.g., cladribine, fludarabine, 6-mercaptopurine, thiamiprine, thiaguanine), pyrimidine analogs (e.g., ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, doxifluridine, emitefur, enocitabine, floxuridine, fluorouracil, gemcitabine, tegafur) fluocinolone, triaminolone, anecortave acetate, fluorometholone, medrysone, and prednislone. In a preferred embodiment, the immunosuppressive agent is dexamethasone. In another preferred embodiment, the immunosuppressive agent is cyclosporin A. In another embodiment, the bioerodible implant comprises more than one immunosuppressive agent.

The implants may further comprise one or more additional therapeutic agents, such as antibiotics or antiinflammatory agents. Specific antibiotics include, but are not limited to:

Antibacterial Antibiotics:

Aminoglycosides (e.g., amikacin, apramycin, arbekacin, bambermycins, butirosin, dibekacin, dihydrostreptomycin, fortimicin(s), gentamicin, isepamicin, kanamycin, micronomicin, neomycin, neomycin undecylenate, netilmicin, paromomycin, ribostamycin, sisomicin, spectinomycin, streptomycin, tobramycin, trospectomycin), amphenicols (e.g., azidamfenicol, chloramphenicol, florfenicol, thiamphenicol), ansamycins (e.g., rifamide, rifampin, rifamycin sv, rifapentine, rifaximin), β-lactams (e.g., carbacephems (e.g., loracarbef), carbapenems (e.g., biapenem, imipenem, meropenem, panipenem), cephalosporins (e.g., cefaclor, cefadroxil, cefamandole, cefatrizine, cefazedone, cefazolin, cefcapene pivoxil, cefclidin, cefdinir, cefditoren, cefepime, cefetamet, cefixime, cefinenoxime, cefodizime, cefonicid, cefoperazone, ceforamide, cefotaxime, cefotiam, cefozopran, cefpimizole, cefpiramide, cefpirome, cefpodoxime proxetil, cefprozil, cefroxadine, cefsulodin, ceftazidime, cefteram, ceftezole, ceftibuten, ceftizoxime, ceftriaxone, cefuroxime, cefuzonam, cephacetrile sodium, cephalexin, cephaloglycin, cephaloridine, cephalosporin, cephalothin, cephapirin sodium, cephradine, pivcefalexin), cephamycins (e.g., cefbuperazone, cefinetazole, cefininox, cefotetan, cefoxitin), monobactams (e.g., aztreonam, carumonam, tigemonam), oxacephems, flomoxef, moxalactam), penicillins (e.g., amdinocillin, amdinocillin pivoxil, amoxicillin, ampicillin, apalcillin, aspoxicillin, azidocillin, azlocillin, bacampicillin, benzylpenicillinic acid, benzylpenicillin sodium, carbenicillin, carindacillin, clometocillin, cloxacillin, cyclacillin, dicloxacillin, epicillin, fenbenicillin, floxacillin, hetacillin, lenampicillin, metampicillin, methicillin sodium, mezlocillin, nafcillin sodium, oxacillin, penamecillin, penethamate hydriodide, penicillin g benethamine, penicillin g benzathine, penicillin g benzhydrylamine, penicillin g calcium, penicillin g hydrabamine, penicillin g potassium, penicillin g procaine, penicillin n, penicillin o, penicillin v, penicillin v benzathine, penicillin v hydrabamine, penimepicycline, phenethicillin potassium, piperacillin, pivampicillin, propicillin, quinacillin, sulbenicillin, sultamicillin, talampicillin, temocillin, ticarcillin), other (e.g., ritipenem), lincosamides (e.g., clindamycin, lincomycin), macrolides (e.g., azithromycin, carbomycin, clarithromycin, dirithromycin, erythromycin, erythromycin acistrate, erythromycin estolate, erythromycin glucoheptonate, erythromycin lactobionate, erythromycin propionate, erythromycin stearate, josamycin, leucomycins, midecamycins, miokamycin, oleandomycin, primycin, rokitamycin, rosaramicin, roxithromycin, spiramycin, troleandomycin), polypeptides (e.g., amphomycin, bacitracin, capreomycin, colistin, enduracidin, enviomycin, fusafungine, gramicidin s, gramicidin(s), mikamycin, polymyxin, pristinamycin, ristocetin, teicoplanin, thiostrepton, tuberactinomycin, tyrocidine, tyrothricin, vancomycin, viomycin, virginiamycin, zinc bacitracin), tetracyclines (e.g., apicycline, chlortetracycline, clomocycline, demeclocycline, doxycycline, guamecycline, lymecycline, meclocycline, methacycline, minocycline, oxytetracycline, penimepicycline, pipacycline, rolitetracycline, sancycline, tetracycline), and others (e.g., cycloserine, mupirocin, tuberin).

Synthetic Antibacterials:

2,4-Diaminopyrimidines (e.g., brodimoprim, tetroxoprim, trimethoprim), nitrofurans (e.g., furaltadone, furazolium chloride, nifuradene, nifuratel, nifurfoline, nifurpirinol, nifurprazine, nifurtoinol, nitrofurantoin), quinolones and analogs (e.g., cinoxacin, ciprofloxacin, clinafloxacin, difloxacin, enoxacin, fleroxacin, flumequine, grepafloxacin, lomefloxacin, miloxacin, nadifloxacin, nalidixic acid, norfloxacin, ofloxacin, oxolinic acid, pazufloxacin, pefloxacin, pipemidic acid, piromidic acid, rosoxacin, rufloxacin, sparfloxacin, temafloxacin, tosufloxacin, trovafloxacin), sulfonamides (e.g., acetyl sulfamethoxypyrazine, benzylsulfamide, chloramine-b, chloramine-t, dichloramine t, n²-formylsulfisomidine, n⁴-β-d-glucosylsulfanilamide, mafenide, 4′-(methylsulfamoyl)sulfanilanilide, noprylsulfamide, phthalylsulfacetamide, phthalylsulfathiazole, salazosulfadimidine, succinylsulfathiazole, sulfabenzamide, sulfacetamide, sulfachlorpyridazine, sulfachrysoidine, sulfacytine, sulfadiazine, sulfadicramide, sulfadimethoxine, sulfadoxine, sulfaethidole, sulfaguanidine, sulfaguanol, sulfalene, sulfaloxic acid, sulfamerazine, sulfameter, sulfamethazine, sulfamethizole, sulfamethomidine, sulfamethoxazole, sulfamethoxypyridazine, sulfametrole, sulfamidochrysoidine, sulfamoxole, sulfanilamide, 4-sulfanilamidosalicylic acid, n⁴-sulfanilylsulfanilamide, sulfanilylurea, n-sulfanilyl-3,4-xylamide, sulfanitran, sulfaperine, sulfaphenazole, sulfaproxyline, sulfapyrazine, sulfapyridine, sulfasomizole, sulfasymazine, sulfathiazole, sulfathiourea, sulfatolamide, sulfisomidine, sulfisoxazole) sulfones (e.g., acedapsone, acediasulfone, acetosulfone sodium, dapsone, diathymosulfone, glucosulfone sodium, solasulfone, succisulfone, sulfanilic acid, p-sulfanilylbenzylamine, sulfoxone sodium, thiazolsulfone), and others (e.g., clofoctol, hexedine, methenamine, methenamine anhydromethylene-citrate, methenamine hippurate, methenamine mandelate, methenamine sulfosalicylate, nitroxoline, taurolidine, xibomol).

Antifungal Antibiotics:

Polyenes (e.g., amphotericin b, candicidin, dermostatin, filipin, fungichromin, hachimycin, hamycin, lucensomycin, mepartricin, natamycin, nystatin, pecilocin, perimycin), others (e.g., azaserine, griseofulvin, oligomycins, neomycin undecylenate, pyirolnitrin, siccanin, tubercidin, viridin).

Synthetic Antifungals:

Allylamines (e.g., butenafine, naftifine, terbinafine), imidazoles (e.g., bifonazole, butoconazole, chlordantoin, chlormidazole, cloconazole, clotrimazole, econazole, enilconazole, fenticonazole, flutrimazole, isoconazole, ketoconazole, lanoconazole, miconazole, omoconazole, oxiconazole nitrate, sertaconazole, sulconazole, tioconazole), thiocarbamates (e.g., tolciclate, tolindate, tolnaftate), triazoles (e.g., fluconazole, itraconazole, saperconazole, terconazole) others (e.g., acrisorcin, amorolfine, biphenamine, bromosalicylchloranilide, buclosamide, calcium propionate, chlorphenesin, ciclopirox, cloxyquin, coparaffinate, diamthazole dihydrochloride, exalamide, flucytosine, halethazole, hexetidine, loflucarban, nifuratel, potassium iodide, propionic acid, pyrithione, salicylanilide, sodium propionate, sulbentine, tenonitrozole, triacetin, ujothion, undecylenic acid, zinc propionate).

Antineoplastic:

Antibiotics and analogs (e.g., aclacinomycins, actinomycin f₁, anthramycin, azaserine, bleomycins, cactinomycin, carubicin, carzinophilin, chromomycins, dactinomycin, daunorubicin, 6-diazo-5-oxo-L-norleucine, doxorubicin, epirubicin, idarubicin, menogaril, mitomycins, mycophenolic acid, nogalamycin, olivomycines, peplomycin, pirarubicin, plicamycin, porfiromycin, puromycin, streptonigrin, streptozocin, tubercidin, zinostatin, zorubicin), antimetabolites (e.g. folic acid analogs (e.g., denopterin, edatrexate, methotrexate, piritrexim, pteropterin, Tomudex®, trimetrexate), purine analogs (e.g., cladribine, fludarabine, 6-mercaptopurine, thiamiprine, thioguanine), pyrimidine analogs (e.g., ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, doxifluridine, emitefur, enocitabine, floxuridine, fluorouracil, gemcitabine, tagafur).

Specific Antiinflammatory Agents Include, but are not Limited to:

Steroidal Antiinflammatory Agents:

21-acetoxypregnenolone, alclometasone, algestone, amcinonide, beclomethasone, betamethasone, budesonide, chloroprednisone, clobetasol, clobetasone, clocortolone, cloprednol, corticosterone, cortisone, cortivazol, deflazacort, desonide, desoximetasone, dexamethasone, diflorasone, diflucortolone, difluprednate, enoxolone, fluazacort, flucloronide, flumethasone, flunisolide, fluocinolone acetonide, fluocinonide, fluocortin butyl, fluocortolone, fluorometholone, fluperolone acetate, fluprednidene acetate, fluprednisolone, flurandrenolide, fluticasone propionate, formocortal, halcinonide, halobetasol propionate, halometasone, halopredone acetate, hydrocortarnate, hydrocortisone, loteprednol etabonate, mazipredone, medrysone, meprednisone, methylprednisolone, mometasone furoate, paramethasone, prednicarbate, prednisolone, prednisolone 25-diethylamino-acetate, prednisolone sodium phosphate, prednisone, prednival, prednylidene, rimexolone, tixocortol, triamcinolone, triamcinolone acetonide, triamcinolone benetonide, and triamcinolone hexacetonide.

Non-Steroidal Antiinflammatory Agents:

Aminoarylcarboxylic acid derivatives (e.g., enfenamic acid, etofenamate, flufenamic acid, isonixin, meclofenamic acid, mefenamic acid, niflumic acid, talniflumate, terofenamate, tolfenamic acid), arylacetic acid derivatives (e.g., aceclofenac, acemetacin, alclofenac, amfenac, amtolmetin guacil, bromfenac, bufexamac, cinmetacin, clopirac, diclofenac sodium, etodolac, felbinac, fenclozic acid, fentiazac, glucametacin, ibufenac, indomethacin, isofezolac, isoxepac, lonazolac, metiazinic acid, mofezolac, oxametacine, pirazolac, proglumetacin, sulindac, tiaramide, tolmetin, tropesin, zomepirac), arylbutyric acid derivatives (e.g., bumadizon, butibufen, fenbufen, xenbucin), arylcarboxylic acids (e.g., clidanac, ketorolac, tinoridine), arylpropionic acid derivatives (e.g., alminoprofen, benoxaprofen, bermoprofen, bucloxic acid, carprofen, fenoprofen, flunoxaprofen, flurbiprofen, ibuprofen, ibuproxam, indoprofen, ketoprofen, loxoprofen, naproxen, oxaprozin, piketoprolen, pirprofen, pranoprofen, protizinic acid, suprofen, tiaprofenic acid, ximoprofen, zaltoprofen), pyrazoles (e.g., difenamizole, epirizole), pyrazolones (e.g., apazone, benzpiperylon, feprazone, mofebutazone, morazone, oxyphenbutazone, phenylbutazone, pipebuzone, propyphenazone, ramifenazone, suxibuzone, thiazolinobutazone), salicylic acid derivatives (e.g., acetaminosalol, aspirin, benorylate, bromosaligenin, calcium acetylsalicylate, diflunisal, etersalate, fendosal, gentisic acid, glycol salicylate, imidazole salicylate, lysine acetylsalicylate, mesalamine, morpholine salicylate, 1-naphthyl salicylate, olsalazine, parsalmide, phenyl acetylsalicylate, phenyl salicylate, salacetamide, salicylamide o-acetic acid, salicylsulfuric acid, salsalate, sulfasalazine), thiazinecarboxamides (e.g., ampiroxicam, droxicam, isoxicam, lornoxicam, piroxicam, tenoxicam), ε-acetamidocaproic acid, s-adenosylmethionine, 3-amino-4-hydroxybutyric acid, amixetrine, bendazac, benzydamine, α-bisabolol, bucolome, difenpiramide, ditazol, emorfazone, fepradinol, guaiazulene, nabumetone, nimesulide, oxaceprol, paranyline, perisoxal, proquazone, superoxide dismutase, tenidap, and zileuton.

The immunosuppressive agent is preferably from about 10 to 90% by weight of the implant. More preferably, the agent is from about 50 to about 80% by weight of the implant. In a preferred embodiment, the agent comprises about 50% by weight of the implant. In a preferred embodiment, the agent comprises about 70% by weight of the implant.

The implants are preferably monolithic i.e. having the immunosuppressive agent homogeneously distributed through the polymeric matrix. In this patent, by homogeneously distributed we mean that the immunosuppressive agent is distributed evenly enough that no detrimental fluctuations in rate of immunosuppressive agent release occur because of uneven distribution of the immunosuppressive agent in the polymer matrix. The selection of the polymeric composition to be employed will vary with the desired release kinetics, the location of the implant, patient tolerance, the nature of the transplant procedure and the like. Characteristics of the polymers will include biodegradability at the site of implantation, compatibility with the agent of interest, ease of encapsulation, water insolubility, and the like. Preferably, the polymeric matrix will not be fully degraded until the drug load has been released. The polymer will usually comprise at least about 10, more usually at least about 20 weight percent of the implant. In one embodiment, the implant comprises more than one polymer.

Biodegradable polymeric compositions which may be employed may be organic esters or ethers, which when degraded result in physiologically acceptable degradation products, including the monomers. Anhydrides, amides, orthoesters or the like, by themselves or in combination with other monomers, may find use. The polymers may be condensation polymers. The polymers may be cross-linked or non-cross-linked, usually not more than lightly cross-linked, generally less than 5%, usually less than 1% cross-linked. For the most part, besides carbon and hydrogen, the polymers will include oxygen and nitrogen, particularly oxygen. The oxygen may be present as oxy, e.g., hydroxy or ether, carbonyl, e.g., non-oxo-carbonyl, such as carboxylic acid ester, and the like. The nitrogen may be present as amide, cyano and amino. The biodegrable polymers set forth in Heller, Biodegrable Polymers in Controlled Drug Delivery, in: CRC Critical Reviews in Therapeutic Drug Carrier Systems, Vol. 1. CRC Press, Boca Raton, Fla. (1987), may be used.

Of particular interest are polymers of hydroxyaliphatic carboxylic acids, either homo- or copolymers, and polysaccharides. Included among the polyesters of interest are polymers of D-lactic acid, L-lactic acid, racemic lactic acid, glycolic acid, polycaprolactone, and combinations thereof. By employing the L-lactate or D-lactate, a slowly biodegrading polymer is achieved, while degradation is substantially enhanced with the racemate. Copolymers of glycolic and lactic acid are of particular interest, where the rate of biodegradation is controlled by the ratio of glycolic to lactic acid. The % of polylactic acid in the polylactic acid polyglycolic acid (PLGA) copolymer can be 0-100%, preferably about 15-85%, more preferably about 35-65%. In a particularly preferred embodiment, a 50/50 PLGA copolymer is used. The most rapidly degraded copolymer has roughly equal amounts of glycolic and lactic acid, where either homopolymer is more resistant to degradation. The ratio of glycolic acid to lactic acid will also affect the brittleness of in the implant, where a more flexible implant is desirable for larger geometries. The size of the polymer particles is preferably about 1-100 μm in diameter, more preferably about 5-50 μm in diameter, more preferably about 9-12 μm in diameter, still more preferably about 10 μm in diameter.

Among the polysaccharides of interest are calcium alginate, and functionalized celluloses, particularly carboxymethylcellulose esters characterized by being biodegradable, water insoluble, a molecular weight of about 5 kD to 500 kD, etc. In one embodiment, the implant comprises hydroxypropyl methylcellulose (HPMC).

Additionally, release modulators such as those described in U.S. Pat. No. 5,869,079 may be included in the implants. The amount of release modulator employed will be dependent on the desired release profile, the activity of the modulator, and on the release profile of the immunosuppressive agent in the absence of modulator.

Other agents may be employed in the formulation for a variety of purposes. For example, buffering agents and preservatives may be employed. Water soluble preservatives which may be employed include sodium bisulfite, sodium bisulfate, sodium thiosulfate, benzalkonium chloride, chlorobutanol, thimerosal, phenylmercuric acetate, phenylmercuric nitrate, methylparaben, polyvinyl alcohol and phenylethyl alcohol. These agents may be present in individual amounts of from about 0.001 to about 5% by weight and preferably about 0.01 to about 2%. Suitable water soluble buffering agents that may be employed are sodium carbonate, sodium borate, sodium phosphate, sodium acetate, sodium bicarbonate, etc., as approved by the FDA for the desired route of administration. These agents may be present in amounts sufficient to maintain a pH of the system of between 2 to 9 and preferably 4 to 8. As such the buffering agent may be as much as 5% on a weight to weight basis of the total composition. Electrolytes such as sodium chloride and potassium chloride may also be included in the formulation. Where the buffering agent or enhancer is hydrophilic, it may also act as a release accelerator. Hydrophilic additives act to increase the release rates through faster dissolution of the material surrounding the drug particles, which increases the surface area of the drug exposed, thereby increasing the rate of drug bioerosion. Similarly, a hydrophobic buffering agent or enhancer dissolve more slowly, slowing the exposure of drug particles, and thereby slowing the rate of drug bioerosion.

The proportions of immunosuppressive agent, polymer, and any other modifiers may be empirically determined by formulating several implants with varying proportions. A USP approved method for dissolution or release test can be used to measure the rate of release (USP 23; NF 18 (1995) pp. 1790-1798). For example, using the infinite sink method, a weighed sample of the drug delivery system is added to a measured volume of a solution containing 0.9% NaCl in water, where the solution volume will be such that the drug concentration is after release is less than 5% of saturation. The mixture is maintained at 37° C. and stirred slowly to maintain the implants in suspension. The appearance of the dissolved drug as a function of time may be followed by various methods known in the art, such as spectrophotometrically, HPLC, mass spectroscopy, etc. until the absorbance becomes constant or until greater than 90% of the drug has been released.

The release kinetics of the drug delivery systems of the invention are dependent in part on the surface area of the implants. Larger surface area exposes more polymer to the eye, causing faster erosion and dissolution of the drug particles entrapped by the polymer. The size and form of the implant can be used to control the rate of release, period of treatment, and drug concentration at the site of implantation. Larger implants will deliver a proportionately larger dose, but depending on the surface to mass ratio, may have a slower release rate. The implants may be particles, sheets, patches, plaques, films, discs, fibers, microcapsules and the like and may be of any size or shape compatible with the selected site of insertion, as long as the implants have the desired release kinetics. Preferably, the implant to be inserted is formulated as a single particle. Preferably, the implant will not migrate from the insertion site following implantation. The upper limit for the implant size will be determined by factors such as the desired release kinetics, location of the implant in the eye, toleration for the implant, size limitations on insertion, ease of handling, etc. For example, the vitreous chamber is able to accommodate relatively large implants of varying geometries, having diameters of 1 to 3 mm. In a preferred embodiment, the implant is a cylindrical pellet (e.g., rod) with dimensions of about 2 mm×0.75 mm diameter. In another preferred embodiment, the implant is a cylindrical pellet (e.g., rod) with dimensions of about 1 mm×380 μm diameter. The implants will also preferably be at least somewhat flexible so as to facilitate both insertion of the implant in the eye and accommodation of the implant. The total weight of the implant is preferably about 50-5000 μg, more preferably about 100-1000 μg. In one embodiment, the implant is about 500 μg. In a particularly preferred embodiment, the implant is about 1000 μg. In another particularly preferred embodiment, the implant is about 120 μg. U.S. Pat. No. 5,869,079 further describes preferred implant sizes for particular regions of the eye, as well as preferred sizes for particular implant shapes.

In a preferred embodiment, a solid bioerodible implant for reducing or preventing transplant rejection in the eye is provided, comprising about 50% by weight of dexamethasone, about 15% by weight of hydroxypropyl methylcellulose (HPMC) and about 35% by weight of polylactic polyglycolic acid (PLGA).

In another preferred embodiment, a solid bioerodible implant for reducing or preventing transplant rejection in the eye is provided, comprising about 70% by weight of dexamethasone and about 30% by weight of polylactic polyglycolic acid (PLGA).

In another preferred embodiment, a solid bioerodible implant for reducing or preventing transplant rejection in the eye is provided, comprising about 50% by weight of dexamethasone and about 50% by weight of polylactic polyglycolic acid (PLGA).

The preferred supplier of PLGA is Boehringer Ingelheim and the preferred PLGA products are Resomer RG 502 and Resomer RG 502H.

In a preferred embodiment, the solid bioerodible implant includes about 50% by weight of dexamethasone, about 15% by weight of hydroxypropyl methylcellulose (HPMC) and about 35% by weight of Resomer RG 502H PLGA.

In a preferred embodiment, the solid bioerodible implant includes about 60% by weight of dexamethasone, about 30% by weight of Resomer RG 502H PLGA, and about 10% by weight of Resomer RG 502 PLGA.

Methods for Making the Implants

Various techniques may be employed to produce the implants. Useful techniques include phase separation methods, interfacial methods, extrusion methods, compression methods, molding methods, injection molding methods, heat press methods and the like.

Choice of the technique and manipulation of the technique parameters employed to produce the implants can influence the release rates of the drug. Room temperature compression methods result in an implant with discrete microparticles of drug and polymer interspersed. Extrusion methods result in implants with a progressively more homogenous dispersion of the drug within the polymer, as the production temperature is increased. When using extrusion methods, the polymer and drug are chosen to as to be stable at the temperatures required for manufacturing, usually at least about 85° C. Extrusion methods use temperatures of about 25° C. to about 150° C., more preferably about 65° C. to about 130° C. Generally, compression methods yield implants with faster release rates than extrusion methods, and higher temperatures yield implants with slower release rates.

In a preferred embodiment, compression methods are used to produce the implants of the invention. Preferably, compression methods use pressures of 50-150 psi, more preferably about 70-80 psi, even more preferably about 76 psi, and use temperatures of about 0° C. to about 115° C., more preferably about 25° C. In another preferred embodiment, extrusion methods are used. Preferably, implants produced by extrusion methods are heated to a temperature range of about 60° C. to about 150° C. for drug/polymer mixing, preferably about 85° C., preferably about 130° C., for a time period of about 0 to 1 hour, 0 to 30 minutes, 5-15 minutes, preferably about 10 minutes, preferably about 0 to 5 min, preferably about 1 hour. Preferably, the implants are then extruded at a temperature of about 60° C. to about 130° C., preferably about 95° C., preferably about 85° C., preferably about 75° C.

U.S. Pat. No. 4,997,652 further describes suitable methods for making the implants of the invention, and is herein incorporated by reference in its entirety.

Kit for the Administration of the Implants

In another aspect of the invention, a kit for treating or preventing transplant rejection in the eye is provided, comprising a bioerodible drug delivery system comprising an immunosuppressive agent and a bioerodible polymer, wherein the drug delivery system is designed to be implanted in the eye. The kit may also include instructions for use.

The bioerodible drug delivery systems as described herein are suitable for use in the kits of the invention. In a preferred embodiment, the immunosuppressive agent is dexamethasone.

The invention is further described by the following nonlimiting examples.

EXAMPLES Example 1 Effect of Dexamethasone Implant in Animal Penetrating Keratoplasty Model

The objective of this study was to determine the efficacy of sustained release intraocular dexamethasone implanted in the anterior chamber of the rat eye at the end of cornea transplant surgery and compare it with local eye drop therapy. The approximately 120 μg dexamethasone implant contained about 15% HPMC, 35% PLGA and 50% dexamethasone, and was prepared and tested in vitro as described in U.S. Pat. No. 5,869,079 (See Example 1), which is specifically incorporated herein by reference in its entirety.

In order to create a very high risk of cornea rejection, a xenograft model was chosen. Mouse cornea from 12 mice of either sex were used as donor tissues for rat.

Eighteen rats of either sex were used in the study. They were divided into 3 groups. Group #1-6 animals received treatment with the dexamethasone implant, Group #2—received treatment with topical steroid and Group #3—control group (without any treatment). Animals were followed up to 8 weeks. After euthanasia eyes were sent for histopathology examination.

TABLE 1 Study design Animal # Group # Eye Treatment 1 1 OD Dex implant 2 1 ″ Dex implant 3 1 ″ Dex implant 4 1 ″ Dex implant 5 1 ″ Dex implant 6 1 ″ Dex implant 7 2 ″ Dex eye drops 8 2 ″ Dex eye drops 9 2 ″ Dex eye drops 10 2 ″ Dex eye drops 11 2 ″ Dex eye drops 12 2 ″ Dex eye drops 13 3 ″ Control (no treatment) 14 3 ″ Control (no treatment) 15 3 ″ Control (no treatment) 16 3 ″ Control (no treatment) 17 3 ″ Control (no treatment) 18 3 ″ Control (no treatment)

Supplies: 0.5% Ophthaine Solution, euthasol solution, ketamine HCl,

Animal Preparation and Surgical Procedure

Obtaining donor corneas: Each mouse was weighed and anesthetized. While under anesthesia, the ophthalmologist collected all donor cornea buttons from mice using trephine. After the procedure mice were euthanized by a lethal dose of Euthasol.

Penetrating keratoplasty (PKP): Each rat was weighed and anesthetized. Using 2.5 mm trephine an initial incision was made in the middle of cornea. The incision was finished using corneal scissors. The anterior chamber (AC) was held using balanced salt solution (BSS). The donor cornea button was attached to the host cornea with 8 interrupted sutures with 11-0 nylon. Before closing the anterior chamber, the dexamethasone implant was implanted into the AC of the first 6 animals.

All eighteen rats survived the procedure. All eyes were examined by an ophthalmologist by slit lamp and all signs of cornea rejection (neovascularization, edema, etc.) were recorded.

In group #2, all animals received 2 drops of Dexamethasone eye drops every day, until the rejection occurred.

Based on clinical observation, rejection of cornea in Group #3. (control) occurred in the first few days after surgery, and by week one 80% of donors' cornea were rejected, by week two 100%. Corneas were showing heavy neovascularization in the first few days followed by corneal edema and total rejection. Group #2 (topical Dexamethasone eye drops) had similar signs observed in this group with some delay. 20% of cornea rejection occurred by week two, 50% by week three, and 80% by week six. At the time of euthanasia (week 8) only 20% were not completely rejected.

However, in group #1, treated with the dexamethasone implant, the corneas did not show any signs of rejection (neovascularization, edema). In all eyes the corneas stayed clear. By the end of the study (week eight) the graft survival was 100%.

Histopathology examination confirmed the clinical observations. In Group #3 heavy inflammation was observed in AC, cornea endothelium, also in the stroma, and some in the epithelium. Corneas also showed edema due to destroyed endothelial cells.

In Group #2 similar findings were observed.

In Group #1, inflammation was totally suppressed by the dexamethasone implant.

The entire clinical and histological finding in this study clearly demonstrated that intraocular sustained release Dexamethasone can prevent corneal rejection in a high-risk xenograft model.

Example 2 Manufacture and In Vitro Testing of Bioerodible Dexamethasone Posterior Segment Drug Delivery System (DEX PS DDS®)

2100 mg of dexamethasone powder (Upjohn) (particle sizes less than 10 μm in diameter) were mixed with 900 mg of 50/50 polylactic acid polyglycolic acid (PLGA) (particle sizes approximately 9-12 μm in diameter) at ambient temperature. A small Teflon® tube was filled with 900-1100 μg of the above mixture, and placed directly on the die cavity. The powder was pushed out of the tubing into the die cavity with a stainless steel wire and the tube and wire were removed from the die. The powder was pressed using a tablet press (approximately 76 psi), ejected with the ejector switch, and removed with tweezers. The resulting pellet was approximately 2 mm×0.75 mm.

Release of dexamethasone from the DEX PS DDS® system was measured. One DDS was placed in a glass vial filled with receptor medium (0.9% NaCl in water). To allow for “infinite sink” conditions, the receptor medium volume was chosen so that the concentration would never exceed 5% of saturation. To minimize secondary transport phenomena, e.g. concentration polarization in the stagnant boundary layer, the glass vial was placed into a shaking water bath at 37° C. Samples were taken for HPLC analysis from the vial at defined time points. The HPLC method was as described in USP 23(1995) pp. 1791-1798. The concentration values were used to calculate the cumulative release data, as shown in Table 2.

TABLE 2 DEX PS DDS ® In vitro Release Day % Total Release 1 10.1 2 16.4 7 39.4 14 55.5 21 69.3 28 80.7 35 88.1

Table 2 shows an almost linear in vitro release of dexamethasone over a one month period of time.

Example 3 In Vivo Testing of DEX PS DDS® in Rabbits

One DEX PS DDS® per eye was implanted into the vitreous of four rabbits with forceps. The in vivo vitreous concentrations of dexamethasone in each of the four eyes were monitored by vitreous sampling. For example, at day 2 the concentrations measured were 0.03 μg/ml, 0.1 μg/ml, 0.33 μg/ml and 0.19 μg/ml. The concentrations in each of the four eyes were measured on days 2, 7, 21, 28 and 35; the average results are summarized in Table 3. The volume of rabbit eyes is approximately 60-70% percent that of human eyes

TABLE 3 In vivo concentrations of dexamethasone (DDS placed with forceps) Day μg/ml 2 0.16 ± 0.13 7 0.15 ± 0.16 21 0.08 ± 0.07 28 0.005 ± 0.01  35 0.037 ± 0.03 

The same DDS was tested in vivo in rabbits, wherein the DDS was placed to a depth of about 5-10 mm in the vitreous with trocar. The levels of dexamethasone in the vitreous are shown in Table 4.

TABLE 4 In vivo concentrations of dexamethasone (DDS placed with trocar) Sample ID 5293-D 5295=D 5293-S 5295-S 5304-D 5306-D 5304-S 5306-S Hours Sample Conc., μg/ml Avg SD 2 0.56 3.07 1.82 1.77 4 5.48 6.95 6.22 1.04 6 2.08 5.15 3.62 2.17 24 2.33 2.69 2.51 0.25 DDS wt. Dex wt. Dex μg/mL Animal#\day μg μg 2 7 14 21 28 35 21427-D 990 693 2.29 21427-S 1023 715.1 1.56 21433-D 804 562.8 1.2 21433-S 1057 739.9 0.77 21428-D 1003 702.1 9.26 21428-S 1025 717.5 0.35 21434-D 863 604.1 3.31 21434-S 1106 774.2 0.84 21429-D 1013 709.1 n/a 21429-S 927 648.9 0.19 21435-D 1104 772.8 0.43 21435-S 941 658.7 0.11 21432-D 860 692 0.43 21432-S 941 685.7 1.72 21436-D 1010 707 0.31 21436-S 1054 737.8 0.13 21431-D 996 697.2 0.52 21431-S 918 642.6 1.15 21437-D 1049 732.9 0.19 21437-D 1075 752.5 0.48 21430-D 994 695.8 0.06 21430-S 1086 760.2 0.18 21438-D 974 681.8 0.03 21438-S 831 581.7 8.35 Ave. 985.17 694.43 1.46 3.44 0.24 0.65 0.59 2.16 * Unable to determine due to insufficient sample

The data indicate that the DEX PS DDS® releases dexamethasone to the vitreous in concentrations above 0.01 μg/ml for an extended period of time. Further, the data indicate that placement of the device with trocar results in much higher levels of drug release than with placement with forceps, most likely due to placement of the device deeper within the vitreous. The data at two, four, six, and 24 hours in Table 4 shows an initial spike of drug release.

Example 4 Manufacture and In Vitro Testing of 50/50 Dexamethasone/PLGA Posterior Segment Drug Delivery System

2.5 g of PLGA (particle sizes approximately 9-12 μm in diameter) were placed in a mixing vessel. The vessel was placed in the oven (130° C.) for ten minutes. 2.5 g of dexamethasone (particle sizes less than approximately 10 μm in diameter) were added to the vessel, and the vessel was returned to the oven for 10 minutes. The PLGA/dexamethasone mixture was mixed well, the blend loaded into a barrel, and 650-790 μm diameter filaments extruded. The resulting filaments were cut into lengths of approximately 0.94 and 1.87 mm for the 500 μg and 1000 μg formulations, respectively.

Release of dexamethasone from the 50/50 dexamethasone/PLGA DDS formulations were measured. One DDS was placed in a glass vial filled with receptor medium (0.9% NaCl in water). To allow for “infinite sink” conditions, the receptor medium volume was chosen so that the concentration would never exceed 5% of saturation. To minimize secondary transport phenomena, e.g. concentration polarization in the stagnant boundary layer, the glass vial was placed into a shaking water bath at 37° C. Samples were taken for HPLC analysis from the vial at defined time points. The HPLC method was as described in USP 23(1995) pp. 1791-1798. The concentration values were used to calculate the cumulative release data, as shown in Tables 5 and 6.

TABLE 5 In vitro release of 50% Dex-PS (0.5 mg formulation) Dex μg Day Release/day % Total release 50% Dex PS 0.5 mg system replicate 1 1 3.00 1.41 7 1.99 7.93 13 0.90 13.43 20 1.79 30.21 27 1.54 49.77 34 1.93 80.52 41 0.24 85.05 48 0.24 90.38 55 0.10 93.00 62 0.15 97.44 69 0.07 99.84 76 0.07 102.25 50% Dex PS 0.5 mg system replicate 2 1 6.00 2.17 7 1.66 6.38 13 0.99 11.05 20 1.21 19.82 27 2.29 42.23 34 2.34 71.05 41 0.44 77.54 48 0.29 82.61 55 0.14 85.34 62 0.20 89.80 69 0.1.0 92.21 76 0.06 84.38 50% Dex PS 0.5 mg system replicate 3 1 5.70 3.27 7 1.11 7.71 13 0.83 13.83 20 0.05 14.47 27 1.63 39.63 34 1.52 69.26 41 0.21 74.10 48 0.19 79.23 55 0.08 81.69 62 0.14 86.58 69 0.07 89.46 76 0.06 92.26

TABLE 6 In vitro release of 50% Dex-PS (1 mg formulation) Dex μg Day Release/day % Total release 50% Dex PS 1 mg system replicate 1 1 6.90 1.28 7 3.48 5.78 13 1.93 10.43 20 3.46 23.22 27 3.74 41.89 34 3.94 66.83 41 1.79 80.17 48 1.28 91.49 55 0.21 93.59 62 0.24 96.39 69 0.11 97.85 76 0.09 99.11 50% Dex PS 1 mg system replicate 2 1 3.90 0.71 7 2.26 3.62 13 1.66 7.57 20 3.14 19.09 27 4.32 40.48 34 4.06 65.77 41 1,61 77.90 48 1.34 89.70 55 0.19 91.60 62 0.23 94.18 69 0.10 95.50 76 0.09 96.78 50% Dex PS 1 mg system replicate 3 1 4.50 0.91 7 2.16 3.98 13 1.69 8.42 20 1.25 13.48 27 3.88 34.67 34 3.53 58.97 41 1.85 74.28 48 0.88 82.85 55 0.19 84.94 62 0.26 88.15 69 0.11 89.75 76 0.10 91.26

Example 5 In Vivo Testing of 50/50 Dexamethasone/PLGA 1 mg Formulations in Rabbits

One 50/50 dexamethasone/PLGA 1 mg formulation DDS per eye was implanted into the vitreous of 6 rabbits using a trocar. The DDS was loaded into the trocar, a hole was punched through the sclera, the trocar inserted through the hole, and the trocar plunger depressed to insert the DDS into the vitreous. In vivo vitreous concentrations of dexamethasone were monitored, as shown in Table 7.

TABLE 7 In vivo vitreous concentrations of dexamethasone Sample ID 5293-D 5295=D 5293-S 5295-S 5304-D 5306-D 5304-S 5306-S Hours Sample Conc., μg/ml Avg SD 2 1.38 1.69 1.54 0.22 4 2.16 0.96 0.47 0.37 6 0.73 0.21 0.47 0.37 24 0.57 0.74 0.66 0.12 Dex μg/mL Animal#\day 7 21 35 49 63 2953-D 0.5 0.58 2953-S 0.11 0.69 2952-D 0.13 1.2 2952-S 0.12 0.55 2946-D  0.19 2.55 2946-S * 3 0.14 2949-D * 5.44 0.28 2949-S  0.0248 0.01 2982-D 1.087 2982-S 0.058 2983-D 0.018 2983-S 0.045 Ave. 0.22  2.16 0.30 0.76 0.75 * High level was due to the surgical artifact

The data indicate that the 50/50 dexamethasone/PLGA DDS releases dexamethasone to the vitreous in concentrations above 0.01 μg/ml for an extended period of time. The data at two, four, six, and 24 hours in Table 7 shows an initial spike of drug release, due to drug which is unencapsulated by the delivery system.

Modifications of the above described modes for carrying out the invention that are obvious to those of ordinary skill in the surgical, pharmaceutical, or related arts are intended to be within the scope of the following claims. 

1. An intraocular, bioerodible drug delivery system comprising a steroid effective in preventing or reducing neovascularization in an eye prone to neovascularization, and a bioerodible polymer selected from the group consisting of hydroxyaliphatic carboxylic acids, and polysaccharides, thereby forming an implant for placement in the interior of an eye prone to neovascularization, wherein: (a) the steroid is dexamethasone and comprises about 50% to 80% of the weight of the drug delivery system; (b) the drug delivery system is configured for placement in the vitreous, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 8 weeks.
 2. The drug delivery system of claim 1, wherein the steroid is the sole active ingredient for preventing or reducing the neovascularization.
 3. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of D-lactic acid.
 4. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of L-lactic acid.
 5. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of racemic lactic acid.
 6. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of glycolic acid.
 7. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of polycaprolactone.
 8. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a calcium alginate.
 9. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of carboxymethylcellulose esters.
 10. The drug delivery system of claim 1, wherein the bioerodible polymer comprises a polymer of hydroxypropyl methylcellulose.
 11. An intraocular, bioerodible drug delivery system comprising particles of dexamethasone and a polylactic acid polyglycolic acid (PLGA) copolymer, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 5 days, and wherein the intraocular, bioerodible drug delivery system is a single pellet or a single extruded filament, and wherein: (a) the dexamethasone comprises about 50% to 80% of the weight of the drug delivery system; and (b) the drug delivery system is configured for placement in the vitreous, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 8 weeks.
 12. The system of claim 11, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 9 weeks.
 13. The system of claim 11, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 10 weeks.
 14. The system of claim 11, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 12 weeks.
 15. The system of claim 11, wherein the system is effective in releasing the dexamethasone into the eye over a period of up to about 6 months.
 16. The system of claim 11, wherein the system is effective in releasing the dexamethasone into the eye over a period of up to about 1 year.
 17. An intraocular, bioerodible drug delivery system comprising a drug effective in preventing or reducing edema in an eye prone to edema, and a bioerodible polymer, wherein: (a) the drug is dexamethasone and comprises about 50% to 80% of the weight of the drug delivery system; and (b) the drug delivery system is configured for placement in the vitreous, wherein the system is effective in releasing the dexamethasone into the eye over a period of at least about 8 weeks.
 18. The drug delivery system of claim 17, wherein the dexamethasone is the sole active ingredient for preventing or reducing the edema.
 19. An intraocular, bioerodible drug delivery system comprising a steroid effective in preventing or reducing neovascularization in an eye prone to neovascularization, and a bioerodible polymer selected from the group consisting of hydroxyaliphatic carboxylic acids, and polysaccharides, thereby forming an implant for placement in the interior of an eye prone to neovascularization, wherein: (a) the steroid is dexamethasone and comprises about 50% to 80% of the weight of the drug delivery system; (b) the drug delivery system is configured for placement in the vitreous, and; (c) the drug delivery system is effective in releasing the drug into the eye over a period of at least about 8 weeks.
 20. The drug delivery system of claim 19, wherein the steroid is the sole active ingredient for preventing or reducing the neovascularization.
 21. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a polymer of D-lactic acid, L-lactic acid, or racemic lactic acid.
 22. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a polymer of glycolic acid.
 23. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a polymer of polycaprolactone.
 24. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a calcium alginate.
 25. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a polymer of carboxymethylcellulose esters.
 26. The drug delivery system of claim 19, wherein the bioerodible polymer comprises a polymer of hydroxypropyl methylcellulose. 